The present invention relates to Titanium alloys, and more particularly, to a process of treating Ti 6-2-2-2-2 alloy to significantly enhance the tensile strength thereof, and to a part so formed.
For many years it has been known that certain metals, such as Titanium, as well as certain metal alloys, exhibit superplasticity within limited temperature ranges and strain rates. Superplasticity is the capability of a material to develop unusually high tensile elongations with a reduced tendency towards necking. Thus when in a superplastic condition, the metal or metal alloy exhibits low resistance to deformation and may be elongated with controlled thinning. This permits a sheet of such metal to be readily formed against dies to achieve desired shapes. Further details of SPF may be had by way of reference to U.S. Pat. No. 3,934,441 of Hamilton et al. entitled "Controlled Environment Superplastic Forming of Metals" and U.S. Pat. No. 3,927,817 of Hamilton et al. entitled "Method of Making Metallic Sandwich Structures."
In the early 1960's the U.S. Air Force funded the development of deep hardenable forging grade alloys. One alloy that was developed is Ti 6Al-2Sn-2Zr-2Cr-2Mo-0.25Si, herein referred to as "Ti 6-2-2-2-2". This alloy has heretofore only been forged and machined into aircraft parts.
Ti 6-4 is currently the Titanium alloy of choice for aerospace applications in the 400.degree.-700.degree. F. temperature range, e.g. adjacent to turbofan engines. It would be desirable to provide an alternative to Ti 6-4 alloy which would provide a higher strength-to-weight ratio.